The invention relates to xerographic process control, and more particularly, to using current sensing technology for automatic exposure correction to compensate for loss of exposure due to contamination of the optical system.
Xerographic control is well known in the prior art. The art is replete with various sensors and systems for charging control, for exposure and illumination control, for developer control, and for measuring toner concentration and adjusting toner dispensers. For example, U.S. Pat. No. 4,348,099 discloses the uses of test patches, an infrared densitometer, and an electrometer for charge, illumination, toner dispenser, and developer bias control. It is also known in prior art machines to automatically compensate for optics contamination by periodically adjusting exposure components.
One difficulty, however, with the prior art systems, has been that the periodic adjustments for contamination usually are part of an overall system reset that is relatively time consuming. For example, during the exposure adjustment to compensate for contamination, usually there is an exposure adjustment for best background suppression and for low density line development. In addition, there is an exposure reset to compensate for changes in dark development potential due to photoreceptor dark decay variation as the photoreceptor ages. During this time, toner test patches fill up the cleaning sump and belt cycles are run without copies being generated. This is an inefficient use of the machine.
It is an object, therefore, of the present invention to provide new and improved automatic exposure reset for contamination compensation that is not part of a comprehensive xerographic system set up. Another object of the present invention is to avoid inefficient component usage in order to automatically reset the exposure system to compensate for optics contamination. Another object of the present invention is to automatically determine illumination levels without the use of toner patches that burden the machine cleaning system. Other objects and advantages of the present invention will become apparent as the following description proceeds, and the features characterizing the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.